The present invention relates to tightening tools such as spanners, screwdrivers or the like by means of which parts may be tightened with a predetermined torque. These tools, which are termed dynamometric, have been known for a long time and attempts have been made to improve them so that they may be more practical in use by providing in the tool electronic display means, for example employing electroluminescent diodes, whereby the value of the torque in fact applied to the part to be tightened may be rendered directly readable.
Although they are more practical than fully-mechanical spanners, these tools still have certain drawbacks.
Firstly, the electronic circuit requires a power supply which, owing to the small amount of space available in the tool, cannot have a large size. Consequently, the autonomy of the tool from the point of view of the electric power supply is small. Secondly, as the display occurs behind a window in the holder of the tool, it is often hidden from view during its use in places which are difficult of access. This is particularly disadvantageous in the case of screwdrivers which are turned during tightening.
Thus, in the course of use, the display is only rarely easily visible to the user.